Rotary pulse generators are known in the art and frequently are mounted to a machine having a rotary shaft. The generator provides an output pulsating signal that varies with the angular velocity of the rotary shaft. The machine frequently takes the form of a motor, although it may take other forms such as a generator or other machine that has a rotating shaft, the speed of which is to be measured. In a motor application, the shaft frequently extends through the motor and protrudes at opposite ends known as the drive end and the anti-drive or accessory end. The pulse generator includes a rotor which is mounted on the accessory end of the motor shaft. The rotor carries on its circumference a pulse generating periodic structure which may include magnetization or an optical pattern. A stator housing is mounted to the motor. The stator housing incorporates a sensor which is spaced radially from the rotor by an air gap, known as the sensor gap. This sensor gap has an optimal distance for proper operation of the sensor for producing output pulses having a frequency corresponding with the angular velocity of the shaft. The sensor gap should be maintained within a close tolerance. The sensor typically includes a wheatstone bridge incorporating resistor elements mounted in a bridge arrangement. The output of such a bridge arrangement is typically a sinusoidal signal which is then converted by suitable electronics into a train of square wave pulses for transmission to counters and controllers and the like. Preferably, the ideal square wave has a 50% duty cycle. The duty cycle is defined as the percentage of time the output signal is high or "ON" relative to the time for one complete cycle of the sinusoidal signal. If the sensor gap is too big, there will be variations in the amplitude of the sinusoidal signal detected, resulting in degradation in the desired duty cycle from 50% or total loss of detecting some or all pulses. On the other hand, if the gap is too small, it could also result in variations in the amplitude of the sinusoidal signal with the same consequences or mechanical interference between the rotor and the stator causing severe damage.
Due to the various manufacturing tolerances involved in producing the rotor and the stator, as well as, similar variations in the manufacture of the motor, variations in the sensor gap may take place from one pulse generator installation to another. This will result in variations in the accuracy of the output signals between various pulse generator installations. In order to adjust the sensor gap of a pulse generator, it has frequently been necessary to remove the pulse generator from the motor. In other situations, at least a cover plate on the stator housing is removed in order to insert a gauge or the like to measure the sensor gap and then introduce special tools for adjusting the sensor gap. Frequently, these adjustments are done by a trial and error technique.
The U.S. Patent to H. Guentner U.S. Pat. No. 4,890,059 presents an example of a digital pulse generator having an adjustable sensor gap. In Guentner, a rotor is mounted to a motor shaft. The rotor carries a magnetic pulse generating pattern on its circumferential surface. A sensor is mounted radially away from the rotor and is spaced therefrom by a sensor gap. A stator housing surrounds and encompasses the rotor and the sensor. The sensor is mounted to the stator housing so as to be adjustable relative thereto for adjusting the size of the sensor gap. A hole is provided in the housing so that a gauge taking the form of a yoke may be inserted into the interior of the housing and then into the sensor gap for adjustment of same. The sensor may be displaced relative to the housing to adjust the sensor gap.